1. Field of the Invention
The invention relates to the field of semiconductor technology. It relates in particular to a method of producing large-area power semiconductor components which comprises the following steps:
(a) production of a semiconductor substrate with a basic doping; PA1 (b) production of a deep-lying pn junction in the semiconductor substrate by implantation of the semiconductor substrate with foreign atoms and subsequently driving the foreign atoms into the semiconductor substrate; and PA1 (c) adjustment of the carrier lifetime by introducing recombination centers into the semiconductor substrate.
2. Discussion of the Background
The basis for producing semiconductor components in general is the systematic introduction of impurities and recombination centers in the form of foreign atoms (in the case of impurities, e.g. Al, As, B, Ga, P; in the case of the recombination centers, e.g. Au or Pt). Especially in the case of semiconductor components intended for high currents and high reverse voltages, pn junctions situated deep in the semiconductor substrate are required. In this case, the introduction of foreign atoms usually splits up into two steps: the implantation of the semiconductor substrate with foreign atoms in the vicinity of the surface and the subsequent drive-in of the foreign atoms into the semiconductor substrate.
Whereas a diffusion process is usually employed for the drive-in, in the state of the art, the implantation usually takes place by means of a gas-phase process and in special cases also by means of a liquid-phase process.
On the other hand, in the production of power semiconductor components irradiation processes are also occasionally used. In this connection, for example, neutron irradiation may be mentioned which results in a phosphorous basic doping via a nuclear transformation in the Si substrate material (so-called neutron transmutation doping). However, ion implantation for the foreign atom implantation or electron, .gamma. or proton irradiation also occasionally find application.
In the case of power semiconductor components with their large substrate areas, maximum utilization of the substrates can only be achieved if properties which are as homogeneous as possible are achieved both inside a single component and also over the entire quantity produced.
Particularly critical are the homogeneity requirements if the target values for the dynamic data of the components are very high, as is the case, for example, in the case of the gate-turnoff thyristor (GTO=Gate Turn Off) which consists of a large number (about 100 to over 1000) of individual thyristors which should all have properties which are as identical as possible.
Conventional (i.e. non-irradiation) methods result in an inhomogeneous distribution of impurity atoms or recombination centers for the following reasons:
doping processes by means of deposition from the liquid or the gaseous phase are supported by flows which result in corresponding inhomogeneities; PA0 certain foreign atoms attach themselves preferably to mostly inhomogeneous defects already present in the crystal (see, for example, M. J. Hill and P. M. Van Iseghem, "Influence of Carbon Concentration on Gold Diffusion in Silicon", Semiconductor Silicon, 1977, pages 715-724). PA0 (1) a neutron irradiation in the form of a neutron transmutation doping which reslts in a homogeneous phosphorous doping of the entire Si substrate via a nuclear reaction for the production of the basic doping. In this process a limitation on the homogeneity results from the distribution of impurities before the irradiation and the intensity distribution of the neutron source. PA0 (2) An ion implantation of, for example, Al, As, B, Ga or P in the form of an implantation in the vicinity of the surface for the implantation of the semiconductor substrate with foreign atoms for the production of a deep-lying pn junction. In this connection a limitation of the homogeneity results from the guidance of the ion beam, which is usually computer-controlled and whose diameter is small in comparison to the diameter of the substrate slice. PA0 (3) An electron, .gamma. or proton irradiation of the semiconductor substrate for the production of recombination centers for adjusting the carrier lifetime. Here, too, the homogeneity limitation is due to the beam guidance.
In the irradiation processes mentioned, these disadvantages do not exist because of the random processes prevailing under these circumstances.
If a single inhomogeneous, traditional process is therefore replaced by an irradiation process (for example, in the case of implantation for doping the p-base of a thyristor deposition from the gas phase by ion implantation), the advantage of greater homogeneity which can in principle thereby be achieved cannot be achieved because inhomogeneities continue to be caused by the other traditional processes.
However, it is precisely the power semiconductor components which are critical from the point of view of production, such as the GTO which rely on as great a homogeneity as possible in the distribution of the impurities and recombination centers. The residual inhomogeneity in these components should be at least less than or equal to 5%, if possible less than or equal to 2%.